Tires typically include treads made of a rubber composition. The rubber comprises various elastomers that are often a combination of cis 1,4-polybutadiene, styrene/butadiene copolymer elastomers, and/or natural rubber, although minor amounts of other elastomers, including, for example, cis 1,4-polyisoprene, isoprene/butadiene and 3,4-polyisoprene, may also be present. When producing rubber compositions for tires, it is common to utilize fillers for the purpose of reducing costs by replacing higher priced constituents of the rubber composition while at the same time imparting some additional functionality or improved properties to the final rubber product. The fillers are conventionally particulate reinforcing fillers of which carbon black and/or aggregates of a synthetic silica such as a precipitated silica are the most common.
The demand for increased traction while maintaining other tire performance properties has been a major focus of tread formulating strategy. The use of low molecular weight oligomers in place of aromatic process oils has also been a central theme. While the use of extending process oils are an inexpensive way to provide good processing and cured rubber performance, their use is decreasing due to raw material availability and recent legislation that requires carcinogenic labeling of certain aromatic oil grades. There is therefore a need for resins that are suitable aromatic oil replacements that are compatible in tire formulations and impart improved physical performance characteristics in the tire.
Resins derived from aliphatic monomers may impart a degree of compatibility with common tire elastomers. However, aliphatic diene monomers have limitations of the Tg achievable using anionic or other polymerization techniques. The challenge is to synthesize compositions with high Tgs yet maintain good compatibility.